A reflective display which requires no light source such as a backlight, for example, a reflective liquid crystal display performs display using an ambient light and consumes a small power. Therefore, this display is often used for portable equipment.
To ensure sufficient brightness of the reflective display, a plate-shaped reflector made of metal such as aluminum or silver with high reflectance could be employed. However, if a surface of the reflector is flat, mirror reflection occurs, thereby causing the light source to be mirrored in the reflector, and portion other than the portion of the reflector in which the light source is mirrored is dark because it reflects little light. So, a displayed image of the display is visually undesirable. Accordingly, if numerous minute concave/convex portions are formed on the surface of the metal reflector to allow the light to be diffused by the concave/convex portions, then such mirroring of the light source is suppressed, and a reflector with preferable reflective characteristics is obtained. The reflective liquid crystal display comprising such reflector is disclosed in Japanese Patents Nos. 2698218, 2756206.
By the way, in the reflector having the concave/convex portions on the surface thereof, a direction of the reflected light depends on a shape of the surface. In the reflector having the concave/convex portions, light is diffracted when reflected. For this reason, when the concave/convex portions are repeated at uniform intervals, lights diffracted by the concave/convex portions on the surface of the reflector interfere with one another, thereby causing the intensified light to be reflected in a specific direction or specific wavelengths to interfere with one another and intensify one another, so that the reflector looks colored. FIG. 19 shows an example of arrangement of such concave/convex shape. FIG. 20 shows a cross section taken along line XX—XX of FIG. 19. In FIG. 19, circles represent concave portions. The concave portions are regularly arranged in a lattice. In FIG. 20, the concave/convex shape is provided in a reflecting film 3 formed by utilizing a concave-convex layer 2 on a substrate 1 and the concave/convex portions in its cross section are regularly repeated. In such regular arrangement, the diffracted lights interfere with one another, thereby causing a visually undesirable display. Accordingly, by irregularly arranging the concave/convex portions in a plane in which the reflector is present, the interference of the diffracted lights is suppressed and the reflected light is white-colored. So, a reflector having a preferable reflection characteristic is obtained.
An example of a method for thus suppressing the interference of the diffracted lights is disclosed in Japanese Patent No. 2912176. In this example, the concave/convex portions are irregularly arranged. Specifically, the concave/convex portions are suitably arranged so that a distribution of distance between adjacent concave portions or between adjacent convex portions, or a distribution of height of concave/convex portions has a variation within a predetermined range. As disclosed in the above-described conventional example, the irregular concave/convex arrangement is capable of preventing the interference of the diffracted lights. However, conventionally, since a specific method for designing the concave/convex arrangement has not been clarified but only how the arrangement is irregular has been clarified, designers of the concave/convex arrangement have had to make trial-and-errors so that variations are within a predetermined range. So when a design of a display having pixels arranged in matrix was changed, for example, the pixel arrangement was changed and a reflector adapted to the changed arrangement was newly designed, the concave/convex arrangement varied. Consequently, an inclination angle on the concave/convex surface varied, and it was impossible to design a reflector having a definite reflection characteristic.
This problem is caused by the interference of the diffracted lights. Therefore, this problem arises in any type of wave including light (light wave),a sound wave, an electromagnetic wave, an oscillating wave, etc. The interference of wave occurs when a wave source is two-dimensionally distributed, or there are many portions having extremal values (local maximum value and local minimum value) of radiation intensity of wave in the two-dimensional wave source. Also, the interference occurs in the wave source having a plane on/through/at which the incident wave is reflected/transmitted/refracted or the like. Therefore, the above-described problem exists in these cases like the reflector of light.